Problem: Simplify the following expression: $k = \dfrac{q}{10} - \dfrac{7q}{4}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10$ and $4$ $\lcm(10, 4) = 20$ $ k = \dfrac{2}{2} \cdot \dfrac{q}{10} - \dfrac{5}{5} \cdot \dfrac{7q}{4} $ $k = \dfrac{2q}{20} - \dfrac{35q}{20}$ $k = \dfrac{2q -35q}{20}$ $k = \dfrac{-33q}{20}$